Using tissue adjacent to carcinoma as a normal control: an obvious but questionable practice

When carcinoma tissue is investigated using biochemical, immunohistochemical, and genetic techniques, adjacent tissue that is macroscopically normal is frequently used as a control, since cancer-related pheno- and geno-typic alterations are assumed to be absent. However, a field that contains genetically abnormal cells surrounds a significant proportion of carcinomas (for example, over 30% of head and neck cancers). These fields can be large (>7 cm in diameter) and consist of cells that are clonally related to the carcinoma. This indicates that adjacent epithelium must be checked for genetic abnormalities before it is considered normal and used as a control for comparison with carcinoma. Copyright (C) 2004 Pathological Society of Great Britain and Ireland. Published by John Wiley Sons, Ltd.